abstract_read_executor: make make_requests() exception safe
abstract_read_executor: make make_requests() exception safe

Message-Id: <3a00fc8d86d1065973c4f56fe9a586a5ec790704@scylladb.com>

scylladb/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla